Patent GB-1191831-A (GB)
Title: Radio Interferometer System
Inventor: ROBINSON STEPHEN JOSEPH
IPC: G01S3/48
Filed: 1965-12-21
Abstract: 1,191,831. Radio direction-finders. MULLARD Ltd. 21 March, 1967 [21 Dec., 1965], No.54085/65. Heading H4D. [Also in Division G4] In a radio direction-finder utilizing two interferometers of different apertures a respective discriminator digitizes the output of each interferometer into a code in which at least for the narrower interferometer only one digit at a time undergoes a transition for values progressing in a given sense of the signal phase difference (and hence of bearing) and logic means is so arranged to combine the outputs of the discriminators in computing a digital final unambiguous direction-denotive output that the information contained in a digit of the discriminator output of the narrower interferometer is not used in computing the final output when the input phase difference to that discriminator is within a designated value of an input phase difference corresponding to a transit of that digit. More than two interferometers may be employed and the invention is applicable to azimuth or elevation determination. If the amplitudes and phases of the two aerials of an interferometer are a, O and b, # respectively a hybrid junction associated with diode square-law detectors and a subtractor gives an output of amplitude 4a b cos #, Fig. 2 (not shown) and by extending this basic arrangement, Fig. 4, outputs E<SP>1</SP> = 4a b cos # and F<SP>1</SP> = - 4a b sin # can be obtained. Further outputs by similar means not shown are G1 = 4a b cos (#+#/4)/#2 and H<SP>1</SP> = 4a b cos (#+3#/4)#2. The zero crossings of outputs E<SP>1</SP>, F<SP>1</SP>, G<SP>1</SP>, H<SP>1</SP> divide the range 0<#<2# into eight equal intervals. Sixteen &c. intervals can be achieved by further manipulation. In the digitization a monophyllic binary code is utilized, positive signals being designated 0 and negative signals, 1 : for example with the discriminator of Fig. 4, when # lies between 3#/4 and # the code - F<SP>1</SP>, - H<SP>1</SP>, E<SP>1</SP>, G<SP>1</SP> gives the binary code 0111 (see Table 1 in the Specification). In a radio direction-finder having a pair of interferometers of spacing ratio n, two digital sets represent phases 2#F 1  and 2#F 2  where F 1 , F 2  are the fractional parts of #/2# and n#/2#, and the logic for producing an unambiguous code over the sector corresponding to a 2# phase difference interval with the narrower interferometer is described, together with schematic diagrams of gate circuits corresponding to the ensuing Boolean algebraic forms. To avoid the use of all digits to resolve ambiguities (signal levels near zero making accurate sign determination impossible) a redundant digital code is provided for the F 1  set. In an embodiment utilizing three interferometers of relative spacings 1 : 4 : 16, Fig. 12, each phase discriminator provides an output corresponding to E<SP>1</SP> . . . H<SP>1</SP> in conjunction with the subtractors indicated, the video amplifiers V are saturated transistor long-tailed pairs to afford a wide dynamic range, and negative pulses at the amplifier outputs trigger bistables M; to avoid spurious triggering of the latter the amplifier outputs are sampled only in the middle of a received pulse by signals from an independent detection channel which incorporates means to open the output gates. Bi-stables M are reset from a differentiator d/d t.